The Collaborative International Dictionary of English v.0.48:

Befoul \Be*foul"\, v. t. [imp. & p. p. Befouled; p. pr. & vb.
   n. Befouling.] [Cf. AS. bef?lan; pref. be- + f?lan to foul.
   See Foul, a.]
   1. To make foul; to soil.
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   2. To entangle or run against so as to impede motion.
      [1913 Webster]